1. Field of the Invention
The present invention relates to HARQ process de-activation in wireless communications systems, and more particularly to a method and related apparatus for keeping a grant of a mobile to be affected by Secondary Absolute Grant messages after the last remaining HARQ process of the mobile is de-activated, so as to reduce signaling overhead of the network and avoid radio resource waste.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting third generation mobile telecommunication technology, the prior art provides High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), which are used to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
HSUPA increases upstream network performance, reduces transmission delay by rapid retransmission of erroneous data transmissions, and can adjust transmission rate based on channel quality. To realize this type of “power control,” HSUPA adopts technologies such as NodeB Scheduling, Hybrid Automatic Repeat Request (HARQ), Soft Handover, and Short Frame Transmission. Correspondingly, the 3rd Generation Partnership Project (3GPP) defines an Enhanced Dedicated Transport Channel (E-DCH) for controlling operations of HSUPA. E-DCH introduces new physical layer channels, such as E-HICH, E-RGCH, E-AGCH, E-DPCCH, and E-DPDCH, which are used for transmitting HARQ ACK/NACK, Uplink Scheduling Information, Control Plane information, and User Plane information. Detailed definitions of the above can be found in the Medium Access Control (MAC) protocol specification, “3GPP TS 25.321 V6.7.0,” and are not given here.
Through Short Frame Transmission technology, HSUPA can configure 2 ms or 10 ms Transmit Time Interval (TTI), and the number of HARQ processes depends on the TTI durations. According to section 11.8.1.1.1 of the aforementioned MAC protocol specification, the number of HARQ processes is equal to the HARQ Round Trip Time (RTT), which is the time duration between the instant when a signaling is sent out and the instant when a response message is received. For 2 ms (millisecond) TTI, the HARQ RTT is equal to 8 TTIs, so the number of HARQ processes is equal to 8. For 10 ms TTI, the HARQ RTT is equal to 4 TTIs, so the number of HARQ processes is equal to 4.
In addition, through NodeB Scheduling technology, a base station (Node B) is allowed to adjust transmission power of mobiles or user equipments (UEs) within its transmission range (cell), so as to control uplink transmission rate of the mobiles. Referring to sections 9.2.5.2.1 and 9.2.5.2.2 of the aforementioned MAC protocol specification, the network can provide Relative Grant (RG) messages and Absolute Grant (AG) messages to a mobile through an E-DCH Relative Grant Channel (E-RGCH) and an E-DCH Absolute Grant Channel (E-AGCH) respectively, so as to adjust the transmission grant of the mobile. The E-AGCH is a shared channel that use an E-DCH Radio Network Temporary Identifier (E-RNTI) in order to address the AG messages to specific mobiles. The AG messages are used to directly adjust the transmission grant of mobiles, and can be classified into two types, Primary and Secondary. The Primary AG message provides an uplink resource grant for a specified mobile served by a cell. The Secondary AG message provides an uplink resource grant for a group of mobiles served by the cell, so as to reduce signaling overhead. On the other hand, the AG message includes an AG value field and an AG scope field. The AG value field indicates the transmission resource the mobile is allowed to use in the next transmission. The AG scope field indicates that the applicability of the AG value is “Per HARQ process” or “All HARQ Processes,” meaning whether the AG value field will affect one or all HARQ processes.
According to section 11.8.1.3.1 of the aforementioned MAC protocol specification, after a mobile receives an AG message, if the E-RNTI type is “Primary,” the AG value is set to “INACTIVE,” the AG scope is “Per HARQ process,” and a 2 ms TTI is configured, then the mobile shall de-activate a current HARQ process, which is the process identified by the value of a variable CURRENT_HARQ_PROCESS. If the E-RNTI type is “Primary,” the AG value is set to “INACTIVE,” the AG scope is “All HARQ processes,” and a secondary E-RNTI was configured by higher layers, then the mobile shall activate all HARQ processes, set Serving Grant (SG) value to stored secondary grant (Serving_Grant=Stored_Secondary_Grant), and set a primary grant state variable to “none” (Primary_Grant_Available=false), meaning that the SG value can be affected by Secondary AG messages. Besides, if the AG value is different from “INACTIVE,” and the E-RNTI type is “Secondary,” then the mobile shall set the variable Stored_Secondary_Grant to the AG value. Oppositely, if the E-RNTI type is “Primary” or the variable Primary_Grant_Available is set to “False,” then the mobile shall set the SG value to the AG value (Serving_Grant=AG value). Note that, definitions of “INACTIVE,” “Stored_Secondary_Grant,” “Primary_Grant_Available,” and “Serving_Grant” can be found in section 3.1.2 of the aforementioned MAC protocol specification.
Therefore, when the Primary AG message sets the AG value to “INACTIVE” and the AG Scope indicates “Per HARQ process” while a 2 ms TTI is configured, the prior art simply de-activates the corresponding HARQ process and keeps the variable Primary_Grant_Available unchanged. The variable Primary_Grant_Available represents whether the SG value is only affected by the Primary AG and RG messages. If Primary_Grant_Available=“True,” the SG value is only affected by the Primary AG or RG messages. If Primary_Grant_Available=“False,” the SG value is affected by the Primary AG, Secondary AG, or RG messages. In such situation, if all the HARQ processes are de-activated, the prior art may waste signaling transmission.
For example, suppose that the mobile has one remaining active process while a 2 ms TTI is configured. Thus, Primary_Grant_Available=“True”. Suppose the serving cell sends a Primary AG message, where the AG value is set to “INACTIVE” and the AG Scope indicates “Per HARQ process”. By the prior art, the variable Primary_Grant_Available is kept to “True” and the remaining active process is deactivated. Since the variable Primary_Grant_Available is “True,” the SG value is only affected by the Primary AG or RG messages. Therefore, the grant provided by earlier Secondary AG messages cannot be used. Furthermore, any future Secondary AG messages will not activate HARQ processes. The only way to activate HARQ processes is through the Primary AG message. As a result, the advantage of the Secondary AG messages vanishes, and signaling overhead is increased.